Biotic interactions underlie ecosystem structure and function, but predicting interaction outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward the equator, using a global experiment with model caterpillars to measure predation risk. Across an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation toward the equator, with a parallel pattern of increasing predation toward lower elevations. Patterns across both latitude and elevation were driven by arthropod predators, with no systematic trend in attack rates by birds or mammals. These matching gradients at global and regional scales suggest consistent drivers of biotic interaction strength, a finding that needs to be integrated into general theories of herbivory, community organization, and life-history evolution.
Bibliographical noteFunding Information:
The Academy of Finland (grants 138346, 276909, and 285803 to T.R.); European Science Foundation (grant 669609 to V.N.); National Science Foundation (grant OPP 0908502 to A.A. and L. Gough, grant DGE-1321846 to C.S.N., and grant 1158817 to E.N.); Instituto de Ecolog?a, A.C. (field work grant to W.D.); Finnish Cultural Foundation, Oskar ?flunds Stiftelse, and Societas Entomologica Helsingforsiensis (grants to T.H.); Natural Environment Research Council (NERC) (grant NE/ J011169/1 to O.T.L.); S?o Paulo Research Foundation (FAPESP) (grant 14/11676-8 to E.N. and grant 13/23457-6 to J. P. Metzger for E.N.); Grant Agency of Czech Republic (grant 14-32024P to K.S., grant 14-04258S to V.N., and grant 14-04258S to A.S.; National Feasibility Program I (LO1208 "TEWEP" to A.S.); Estonian Ministry of Education and Research (grant IUT20-33 to T.T.); and Norwegian Research Council's Climate Change and Impacts in Norway (NORKLIMA) program (grant 230607/E10 to V.V.).
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